This invention pertains generally to compact antenna ranges, and more particularly to an improved anechoic chamber in which radiation patterns may be measured using radio frequency (R.F.) energy having substantially uniform and free of distortion wavefronts.
It is known in the art that anechoic chambers are used to determine the antenna pattern of a test antenna. The test antenna, mounted on a test antenna mounting surface on the anechoic chamber, is illuminated by a test signal comprised of R.F. energy from a source antenna located in the anechoic chamber. The R.F. energy produced by the source antenna has a wavefront having near-field characteristics, meaning a wavefront not having uniform amplitude and phase. The area illuminating the aperture of the test antenna, also known as a "quiet zone," typically is illuminated by the near-field wavefront. A resultant antenna pattern of the test antenna may not be accurate due to the lack of uniform amplitude and phase of the energy in the quiet zone. Various techniques have been attempted without success to create a wavefront in the quiet zone having far-field characteristics, meaning a wavefront having uniform amplitude and phase.
Another deficiency of any known type of anechoic chamber is that a design useful for any given frequency of R.F. energy is probably not useful at a different frequency. That is to say, known types of anechoic chambers are narrow band devices. Further, it is not possible for adapt any known anechoic chamber to use at a frequency other than its design frequency simply by scaling dimensions.